Not necessarily. If the engine is now smoking more than it has in the past, and everything else is exactly the same (same fuel, plug, conditions, etc), then your engine is probably running a little more rich than it has previously. But the amount of smoke is not an absolute indicator that an engine is running overly rich. Different fuels will smoke differently when the engine's properly-adjusted. Get the engine adjusted properly, and then see what kind of smoke trail you get. If the fuel smokes a lot, even though the engine's running well, your fuel has an oil that encourages smoke. Don't worry about the amount of smoke output, and never sacrifice your engine's oil intake just to minimize the 'vapor trail' it leaves when operating.

This article is from Duratrax.